distillation column design and McCABE-THIELE DESIGN METHOD

1. S.N.PATEL INSTITUTE OF TECHNOLOGY AND RESEARCH
CENTRE,UMRAKH
Name :- Patel Meet J.
Pan No :- 150490105035
Topic :- McCABE-THIELE DESIGN METHOD
Subject :- PED-1 ( 2160503)

2. Distillation Column Design:-
 As mentioned, distillation columns are designed using VLE data for the mixtures to
be separated.
 The vapour-liquid equilibrium characteristics (indicated by the shape of the
equilibrium curve) of the mixture will determine the number of stages, and hence
the number of trays, required for the separation.
 This is illustrated clearly by applying the McCabe-Thiele method to design a
binary column.

3. McCABE-THIELE DESIGN METHOD:-
 The McCabe-Thiele approach is a graphical one, and uses the VLE plot to determine
the theoretical number of stages required to effect the separation of a binary mixture.
 It assumes constant molar overflow and this implies that:
1) p molal heats of vaporisation of the components are roughly the same.
2) p heat effects (heats of solution, heat losses to and from column, etc.) are
negligible.
3) p for every mole of vapour condensed, 1 mole of liquid is vaporised.
 The design procedure is simple. Given the VLE diagram of the binary mixture,
operating lines are drawn first.

4.  Operating lines define the mass balance relationships between the liquid and
vapour phases in the column.
1) p There is one operating line for the bottom (stripping) section of the column,
and on for the top (rectification or enriching) section of the column.
2) p Use of the constant molar overflow assumption also ensures the the operating
lines are straight lines.

5. Operating Line for the Rectification section:-
 The operating line of the rectification section is constructed as follows.
 First the desired top product composition is located on the VLE diagram , and a
vertical line produced until it intersects the diagonal line that splits the VLE plot in
half.
 A line with slope with R/(R+1) is then drawn from this instersection point as shown
in the diagram below.

6.  R is the ratio of reflux flow (L) to distillate flow (D) and is called the reflux ratio and
is a measure of how much of the material going up the top of the column is
returned back to the column as reflux.

7. Operating Line for the Stripping Section:-
 The operating line for the stripping section is constructed in a similar manner.
However, the starting point is the desired bottom product composition. A vertical
line is drawn from this point to the diagonal line, and a line of slope Ls/Vs is drawn
as illustrated in the diagram below.
 Ls is the liquid rate down the stripping section of the column, while Vs is the vapour
rate up the stripping section of the column. Thus the slope of the operating line for
the stripping section is a ratio between the liquid and vapour flows in that part of
the column.

9. Thank You